Wearable display for near-to-eye viewing

ABSTRACT

An optical apparatus has a laser source to direct modulated light toward a scan mirror and objective lens that define a focal surface. Pupil relay optics relay a first pupil at the scan mirror to a second pupil at an eye lens, the pupil relay optics defining an optical axis extending between pupils and having a curved mirror that transmits substantially half of the modulated beam and that has a first center of curvature at the first pupil and a first polarizer in the path of light from the scan mirror to reflect incident light of a first polarization and first angle toward the curved mirror surface and transmit incident light of an orthogonal polarization and second angle, wherein the pupil relay optics direct the modulated light beam twice to the first polarizer, and wherein the modulated light incident the second time is collimated and directed toward the second pupil.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional application Ser.No. 62/426,655, provisionally filed on Nov. 28, 2016 entitled “WEARABLEDISPLAY FOR NEAR-TO-EYE VIEWING” in the names of David Kessler et al.,incorporated herein in its entirety.

TECHNICAL FIELD

The present invention relates generally to near-to-eye displays and moreparticularly to a display that employs an imaging apparatus that employsa pupil relay configuration having concentric design.

BACKGROUND

There have been a number of solutions proposed for providing imagecontent from wearable devices. Various types of goggles, glasses, andother apparatus have been described for displaying image content to aviewer who is wearing the apparatus. These devices may be completelyimmersive, so that the viewer sees only images generated by theapparatus and has no ability to see the outside world when wearing thedevice, thus providing virtual reality (VR) display. Alternately,varying degrees of visibility of the real world are provided with otherdesigns, so that the generated images are superimposed on the real-worldimage as an augmented reality (AR) or mixed reality display or, in someway, used to complement the real-world visual content that lies in theviewer's field of view.

Wearable display devices offer considerable promise for providinginformation and displaying complementary imagery that can improveperformance and efficiency in a number of fields and can help to enhancea viewer's understanding of visual content that lies in the field ofview. In medicine and dentistry, for example, the capability to viewimage content that had been previously stored and, optionally, postprocessed, or is currently being acquired from another vantage point canhelp the practitioner to more accurately obtain detailed data that wouldaid diagnosis and treatment. Imaging data that is currently availableonly from high-cost 3-D imaging systems can be provided in a usableformat for viewing on less expensive wearable imaging equipment thatallows the practitioner to have this information in an active clinicalsetting. Stereoscopic imaging, with its enhanced spatial understandingand improved presentation of relevant detail, can be particularly usefulfor those treating patients using medical imaging guidance or medicaldata, as well as for those skilled in other fields. In addition, eventhe presentation of non-stereoscopic 2-D image content, provided byeyewear that allows clear visibility of the primary visual field withoutobstruction, can be useful for various functions, including uses inpatient monitoring as well as tele-medicine and in remote diagnostic ortherapeutic guidance, for example.

With many of the apparatus that have been proposed for wearabledisplays, the viewer is encumbered by the device in some way, due todevice size, bulkiness and discomfort, component and image positioning,poor image quality, eye fatigue, and other difficulties. Although manyclever solutions for providing a more natural viewing experience havebeen outlined, and a number of advances toward improved image qualityhave been introduced, the form factors for many of these solutions stillmake it difficult to win broad-based acceptance for these devices,particularly for long-term use or during work or recreational activity.Their bulky size and appearance are still considered to be significantfactors in limiting the appeal of wearable imaging devices for manypeople.

Despite years of design effort and optimization, including integrationof miniaturization and improved imaging technologies, designing wearabledisplay apparatus with acceptable ergonomics and high image quality hasproved to be a continuing challenge. Workable solutions for wearabledisplay devices that have a natural “feel” and that can be easily wornand used remain elusive. Thus, it can be appreciated that there is aneed for a wearable device for single-eye or stereoscopic display thatprovides high image quality and is lightweight, is inexpensive, easy touse, and ergonomically less invasive and cumbersome than conventionaldesigns and provides enhanced display opportunities without obstructingor diminishing the primary visual field.

SUMMARY

It is an object of the present invention to advance the art of direct,virtual retinal display, more generally known as virtual imagepresentation for virtual or augmented reality viewing from a wearableapparatus. Embodiments of the present disclosure provide a wearableviewing apparatus that provides suitable image quality with little or noimpediment to viewer visibility over the field of view. Embodiments ofthe present disclosure can provide an improved viewing apparatus thatreduces a number of optical, physiological, and ergonomic constraints ofconventional head-mounted displays (HMDs). Embodiments of the presentdisclosure can provide a wearable viewing apparatus having increasedfield of view with versatile arrangements of scanning, beam widthadjustment, and related optical components in an ultra-near-to-eyeimaging arrangement, including embodiments with optical componentswithin the object focal length of the eye.

These objects are given only by way of illustrative example, and suchobjects may be exemplary of one or more embodiments of the invention.Other desirable objectives and advantages inherently achieved by thedisclosed invention may occur or become apparent to those skilled in theart. The invention is defined by the appended claims.

According to one aspect of the present disclosure, there is provided anoptical apparatus for near-eye viewing comprising:

-   -   a laser light source energizable to direct a beam to a scan        mirror;    -   a curved mirror surface optically concentric with the scan        mirror and partially transmissive;    -   a first polarizer disposed between the scan mirror and the        curved mirror surface, the first polarizer having a first        polarization axis;    -   a quarter wave plate disposed between the polarizer and the        curved mirror surface;    -   a second polarizer disposed downstream from the curved mirror        and having a second polarization axis that is orthogonal to the        first polarization axis.

According to an alternate aspect of the present disclosure, there isprovided an optical apparatus worn by a viewer and comprising:

-   -   a laser light source energizable to direct a modulated beam        toward a scan mirror;    -   an objective lens in the path of the modulated beam directed        toward the scan mirror,    -   wherein the objective lens and the scan mirror define a curved        focal surface for the modulated beam;    -   pupil relay optics disposed to relay a first pupil at the scan        mirror to a second pupil at an eye lens of the viewer, the pupil        relay optics defining an optical path that extends along an        optical axis between the first and second pupils, the optical        path comprising:        -   (i) a curved mirror surface disposed to transmit            substantially half of the light incident from the modulated            beam and that has a first center of curvature at the first            pupil; and        -   (ii) a first polarizer disposed in the optical path to            receive light from the scan mirror and formed to reflect            incident light of a first polarization toward the curved            mirror surface and to transmit incident light of a second            polarization, orthogonal to the first polarization, wherein            the optical path defined by the pupil relay optics directs            the modulated light beam twice to the first polarizer, and            wherein the modulated light beam incident the second time on            the first polarizer is collimated and directed toward the            second pupil.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of the embodiments of the invention, as illustrated in theaccompanying drawings. The elements of the drawings are not necessarilyto scale relative to each other.

FIG. 1A is a schematic top view that shows the horizontal field of viewof a viewer.

FIG. 1B is a schematic side view that shows the vertical field of viewof a standing viewer looking forward, with normal and peripheral fieldsof view.

FIG. 1C is a schematic side view that shows the vertical field of viewof a seated viewer looking forward, with normal and peripheral fields ofview.

FIG. 1D is a cross section view showing portions of the eye and objectand image focal lengths of the eye.

FIG. 1E is a schematic diagram that shows components of an image sourceaccording to an embodiment of the present disclosure.

FIG. 1F is a schematic diagram showing a conventional “pancake” designfor an eyepiece of an imaging apparatus.

FIG. 2A is a perspective view that shows components of a pupil relay inan imaging apparatus for near-eye viewing according to an embodiment ofthe present disclosure.

FIG. 2B is a side view that shows components of an imaging apparatus fornear-eye viewing according to a pupil relay embodiment of the presentdisclosure.

FIG. 2C is a side view of an alternate embodiment of a pupil relay fornear-eye viewing.

FIGS. 3A and 3B are schematic views showing input optics for scanningand prefocusing according to an embodiment of the present disclosure.

FIG. 3C lists surface and lens characteristics for the input optics.

FIG. 4A shows a side view of a configuration for an imaging apparatusfor near-eye viewing using a pupil relay with a “pancake” opticalconfiguration.

FIG. 4B lists surface and lens characteristics for the refractiveconfiguration of FIG. 4A.

FIG. 4C shows a perspective view of configuration for an imagingapparatus for near-eye viewing using a pupil relay.

FIG. 4D shows a side view of the configuration of FIG. 4A.

FIG. 4E shows a top view of the configuration of FIG. 4A.

FIG. 4F shows the system with a folded optical path.

FIG. 4G is an exploded side view of the configuration of FIG. 4A.

FIG. 4H is a perspective view of the configuration of FIG. 4A.

FIG. 4I is a perspective view of the configuration of FIG. 4A.

FIGS. 5A and 5B show side and front views, respectively, of an imagingapparatus on the face of a viewer.

FIGS. 6A and 6B show schematic side views of an imaging apparatusemploying a pupil relay according to an alternate embodiment of thepresent disclosure.

FIG. 6C shows a perspective view of a pupil relay in an imagingapparatus according to another embodiment of the present invention.

FIG. 6D shows a side view of an imaging apparatus.

FIGS. 7A-7D show different views of an imaging apparatus relative to theviewer's eye.

FIG. 8A shows schematic side view of a symmetrical arrangement with abeam splitter used to correct distortion.

FIG. 8B shows a perspective exploded view of the arrangement of FIG. 8A.

FIG. 8C shows keystone distortion that can occur due to scanning for theembodiment of FIG. 4A if not corrected.

FIG. 8D shows correction achieved for this distortion.

DETAILED DESCRIPTION

Figures provided herein are given in order to illustrate principles ofoperation and component relationships along their respective opticalpaths according to the present invention and are not drawn with intentto show actual size or scale. Some exaggeration may be necessary inorder to emphasize basic structural relationships or principles ofoperation. Some conventional components that would be needed forimplementation of the described embodiments, such as support componentsused for providing power, for packaging, and for mounting, for example,are not shown in the drawings in order to simplify description of theinvention. In the drawings and text that follow, like components aredesignated with like reference numerals, and similar descriptionsconcerning components and arrangement or interaction of componentsalready described may be omitted.

Where they are used, the terms “first”, “second”, and so on, do notnecessarily denote any ordinal or priority relation, but may be used formore clearly distinguishing one element or time interval from another.The term “plurality” means at least two.

In the context of the present disclosure, the term “energizable”describes a component or device that is enabled to perform a functionupon receiving power and, optionally, upon also receiving an enablingsignal.

In the context of the present disclosure, positional terms such as “top”and “bottom”, “upward” and “downward”, and similar expressions are useddescriptively, to differentiate different surfaces or views of anassembly or structure and do not describe any necessary orientation ofthe assembly in an optical apparatus. The terms “upstream” and“downstream” as used herein have their conventional usage and refer torelative positions of light or light-conditioning or redirectingcomponents as the light proceeds along an optical path.

In the context of the present disclosure, the term “coupled” is intendedto indicate a mechanical association, connection, relation, or linking,between two or more components, such that the disposition of onecomponent affects the spatial disposition of a component to which it iscoupled. For mechanical coupling, two components need not be in directcontact, but can be linked through one or more intermediary components.

In the context of the present disclosure, the term “left eye image”describes a virtual image that is formed in the left eye of the viewerand a “right eye image” describes a corresponding virtual image that isformed in the right eye of the viewer. The phrases “left eye” and “righteye” may be used as adjectives to distinguish imaging components forforming each image of a stereoscopic image pair, as the concept iswidely understood by those skilled in the stereoscopic imaging arts.

An optical pupil relay system defines an optical axis and an opticalpath that transfers a beam incident at a first pupil at a first positionto a second pupil position. That is, the scanned beams coming out of theaperture at the first position are all directed to overlap at the secondposition, with possible magnification. In embodiments of the presentdisclosure, no pupil magnification is required; pupil relay opticsdescribed herein can be 1:1 relays. Additional magnification can beprovided, however. The beam angles are not identical at the respectivefirst and second pupil positions; at the input pupil to the relaysystem, beams are divergent and at the output pupil, beams arecollimated. In a pupil relay system, the input and output pupils areclearly defined by the optical components.

It is well known that optical systems have two sets of conjugatesurfaces. A first set of conjugate surfaces comprises the object andimage surfaces of the optical system; a second set of conjugate surfacescomprises the entrance pupil and the exit pupil. By default, whenimaging is discussed, it is understood that the conjugate surfaces arethe object and the image surface. The term “pupil relay”, as used in theoptical arts and in the instant disclosure, is used to emphasize thatthe main function of the optical system is to image the entrance pupilto the exit pupil. Imaging can be achieved using pupil relay optics;however, the principles of operation are based on relay of a first pupilto a second pupil, as is familiar to those skilled in the optical designarts.

The requirements for aberration correction for an optical system differ,depending on whether the system is an object-to-image imager or a pupilrelay. Since an imaging system is commonly used with incoherent light,phase differences between object points is of little or no interest. Ina pupil relay, however, the phase at the entrance pupil is aconsideration. Typically, a pupil relay accepts a collimated beamcentered at the entrance pupil at some field angle, and provides anoutput beam, usually collimated and centered at the exit pupil, and withno degradation of the phase of the input beam.

Two sets of aberrations may need to be corrected, corresponding to thetwo sets of conjugates, as is well known to those skilled in opticaldesign. Among those skilled in optics, the set of aberrations associatedwith the conjugation of the entrance pupil to the exit pupil are termed“pupil aberrations”. For example, a well known imaging system is the“Offner system” disclosed in U.S. Pat. No. 3,748,015 to Offner entitled“Unit Power Imaging Catoptric Anastigmat”. The Offner system is designedto be corrected over an arc at the image plane. It is not corrected,however, as a relay, and an incoming collimated beam, even if on axis,will be strongly degraded. U.S. Pat. No. 8,274,720 by Kessler, entitled“Concentric Afocal Beam Relay,” discusses the steps and significantmodifications needed for conversion of the Offner imager to an afocalpupil relay.

It is noteworthy that most pupil relays are afocal. That is, for pupilrelays, both the input beam and the output beam are collimated. Thesystem typically has no power but is usually composed of two groups,both with optical power, wherein each of the groups of optics is focal.The combination of the two groups results in an afocal relay in the sameway that an afocal Keplerian telescope is composed of two positivegroups with an intermediate focal plane, where the two groups aresignificantly separated by their two focal distances.

Pupil relays for embodiments of the present disclosure are focal. Afocal pupil relay defines an optical path that accepts a focused inputbeam and outputs a collimated beam. In general, the focal pupil relayincludes multiple lens elements and related optical components that canbe formed into a small number of groups, with grouped elements cementedtogether or clustered together in close proximity. This characteristicmakes the focal pupil relay compact, when compared to afocal relays thatuse separated groups, such as mirrors. An example of an afocal relay isgiven in US Patent Application Publication No. 2011/0242635 by Oka. Itshould be noted that the optical path tracks the optical axis, but isnot necessarily collinear with the optical axis at each point. Theoptical axis can be a single, undeviated line that connects the twopupils or may be folded and have a number of line segments havingdifferent directions, such as using mirrors or reflective polarizeroptics, as described in subsequent embodiments.

A characteristic of the pupil relay, as compared with imaging optics ingeneral, is that the input and output pupils are clearly defined by theoptical system geometry. The focal pupil relay optics of the presentdisclosure performs two functions of particular significance to theimaging task: (i) conjugates the entrance pupil, at which a scannermirror is positioned, with the exit pupil, at the position of the irisof the viewer's eye; and (ii) collimates the curved input focal surface.

By comparison with the focal pupil relay, an afocal relay provides onlythe first function (i), conjugation of entrance and exit pupils.Collimation is not provided with the afocal relay, since the input beamis already collimated and the relay system has no optical power.

The term “oblique”, where used in the present disclosure, describes anangular relationship that is not parallel or normal, that is, other thanan integer multiple of 90 degrees. In practice, two optical surfaces areconsidered to be oblique with respect to each other if they are offsetfrom parallel or normal by at least about +/−2 degrees or more.Similarly, a line and a plane are considered to be oblique to each otherif they are offset from parallel or normal by at least about +/−2degrees or more. Substantially parallel planes are parallel to within+/−2 degrees. Likewise, substantially parallel beams are parallel towithin about +/−2 degrees.

In the context of the present disclosure, the term “about”, when usedwith reference to a measurement, means within expected tolerances formeasurement error and inaccuracy that are accepted in practice. Somereasonable tolerance must be allowed, for example, for measurementdifferences in determining the extent of a particular viewer's visualfield, as it would vary from the measurement of one practitioner toanother.

Microelectromechanical systems (MEMS) devices include a number ofmechanical components that provide systems of miniaturized mechanicaland electromechanical elements (that is, devices and structures) thatare made using microfabrication techniques analogous to those used forforming semiconductor devices. MEMS devices can vary from relativelysimple structures having no moving elements, to extremely complexelectromechanical systems with multiple moving elements under thecontrol of integrated microelectronics. In a MEMS device, at least someof the elements have a mechanical function, whether or not the elementsare themselves movable. MEMS devices can alternately be termed“micro-machined devices” or devices formed and operating usingmicrosystems technologies. Physical dimensions of individual MEMSelements can range from well below one micron to several millimeters. Inthe context of the present disclosure, MEMS devices provide mechanicallymovable elements, such as reflectors, that are energizable to temporallyand spatially modulate light in order to provide a virtual image using araster scan pattern.

In contrast to methods for forming a real image, a virtual image is notformed on a display surface. That is, if a display surface werepositioned at the perceived location of a virtual image, no image wouldbe formed on that surface. A virtual image is formed by an opticalsystem that also determines viewing parameters such as far point,apparent angular width, and other characteristics. Virtual image displayhas a number of inherent advantages for augmented reality and virtualreality viewing. For example, the size of a virtual image is not limitedby the size or location of a display surface. Additionally, the sourceobject for a virtual image may be small; a magnifying glass, as a simpleexample, provides a virtual image of its object. It is known that, incomparison with systems that project a real image, a more realisticviewing experience can be provided by forming a virtual image that isdisposed to appear some distance away. Providing a virtual image usingonly modulated light also obviates any need to compensate for screen orother display artifacts, as may be necessary when forming a real image.

In conventional use, the term “field of view” (FOV) broadly relates tothe overall visual field that is available to a viewer with relativelynormal eyesight under daylight viewing conditions. Field of view istypically measured in orthogonal horizontal and vertical directions.FIG. 1A shows how angular portions of the horizontal field of view aredefined according to the present disclosure. Horizontal monocular visuallimits are generally considered to be slightly in excess of 120 degrees,centered about a central horizontal line of sight S1, as bounded betweenlines 16 and 18. Symbol recognition in the horizontal FOV is generallyconsidered to be in the area about +/−30 degrees from horizontal line ofsight S1, as bounded between lines 56 and 58.

The vertical field of view, as this measurement is referred to herein,is shown schematically in FIG. 1B. A horizontal line of sight S1 isdefined, extending generally at about 0 degrees to horizontal for aviewer who is standing, varying from true horizontal by no more thanabout +/−2 degrees. The horizontal line of sight has been defined as theprimary position of the eyes with the retinal plane co-planar with thetransverse visual head plane. This plane is defined by the principalretinal plane of the eye, the oculomolar nucleus and the calciminecortex. It is defined as having a constant relationship to thecanthomeafal line and perpendicular to Listing's plane. The fullvertical FOV for an adult viewer having normal vision generally extendsfrom about 60 degrees above (expressed as +60 degrees) to about 75degrees below horizontal (expressed as −75 degrees); the normal “usable”vertical field of view (FOV) F1 for display of a virtual image istypically considered to be defined within the range of angles from +25degrees above to −30 degrees below the horizontal line of sight S1.

Different portions of the field of view can be distinguished from eachother. Foveal vision, having the highest visual acuity due to thegreatest retinal cone density, encompasses the central portion of thehuman visual field. This region uses approximately 50% of our opticalpathway. Parafoveal vision, providing high quality acuity and colorvision as well, due to a high retinal cone concentration, is thusgenerally considered to be at an angle α that is within no more thanabout +/−5 degrees of the line of sight. The approximately ten-degreeparafoveal visual field is generally circular about the line of sightwith about a four-inch diameter at a distance of 22 inches. As anapproximation for an adult viewer, this region would be slightly smallerthan the surface of a standard compact disc (CD) or digital video disc(DVD) held out at arm's length. Outside of this region, the visual fieldis considered to be peripheral and provides increasingly less visualinformation. Due to the retinal rod distribution of the human eye, thebulk of peripheral visual information lies within about the first 20degrees beyond the parafoveal field of view.

For the embodiments described herein, a normal usable vertical FOV F1 islarger than the parafoveal FOV and is defined as being within the rangefrom about +25 to −30 degrees of the line of sight. FOV F1 is consideredgenerally to be within the limits of color discrimination, whichdegrades substantially for vision angles increasingly outside thisregion. FIGS. 1B and 1C show the lower portion of the normal verticalFOV F1, below forward horizontal line of sight S1, as bound within anangle θ of horizontal line of sight S1. The region that lies within the+60 to −75 degree vertical visual limits of the viewer but in theregions above or below the normal vertical FOV F1 is considered to bethe “vertical peripheral vision” field or, simply, a peripheral verticalfield with upper and lower portions F2A, F2B, respectively.

FIG. 1B shows the two portions of the peripheral vertical field, anupper portion F2A above the line of sight S1 and a corresponding lowerportion F2B below horizontal line of sight S1. Upper portion F2A liesbetween about 60 degrees from line of sight S1, shown by a line 12, andthe upper definition of FOV F1 which is about 25-30 degrees above lineof sight S1. A lower portion F2B of the peripheral vertical field liesbelow FOV F1 which extends down to about −30 degrees; portion F2B isbounded by about −75 degrees from line of sight S1, shown by a line 14.Thus, lower portion F2B of the peripheral vertical FOV lies betweenabout −30 and −75 degrees relative to horizontal light of sight S1.

Line of sight S1 generally tracks head position. For a seated viewer,for example, the reference line of sight S1 tends to shift downwards toabout 15 degrees from horizontal. All of the other vertical coordinatesand angles that define parafoveal and peripheral fields shiftaccordingly, as is shown schematically in FIG. 1C. In the context of thepresent disclosure, the reference line of sight S1 for vertical fieldsis considered to correspond to the horizontal for a standing viewer,tilted to about 15 degrees from horizontal for a seated viewer. Thisline of sight is termed a horizontal line of sight in the descriptionthat follows.

As shown in the cross-sectional side view of FIG. 1D, the optics systemof the human eye E, considered as an optical component primarily withlens 24 and cornea 28, has focal lengths that are determined by thegeometry of the lens 24, cornea 28, and the surrounding medium. For anadult with normal, uncorrected vision, the eye E has a front focallength F_(o) of about 16.7 mm. The normal, uncorrected adult human eye Ehas a rear focal length F_(i) of about 22.3 mm. The front focal lengthF_(o) is in air; the rear focal length F_(i) is within the refractiveliquid medium of the eye E, which effectively shortens the actualoptical distance dimensions as shown in FIG. 1D. The iris, which formsthe pupil of the eye as an imaging system and limits the aperture toless than about 7 mm, is not shown for clarity in FIG. 1D. Under brightlight conditions, the pupil diameter controlled by the iris averagesonly about 2.5 mm. A “normal” eye can focus parallel light rays from adistant object onto the retina 26, with the parallel rays considered tobe at infinity, to a point on the retina 26 at the back of the eye E,where processing of the visual information begins. As an object isbrought close to the eye E, however, the muscles change the shape of thelens 24 so that rays form an inverted real image on the retina 26. Thetheoretical region of focus in front of the lens is the object imagezone.

The schematic block diagram of FIG. 1E shows components of an imagegenerator 212 for forming a modulated beam according to an embodiment ofthe present disclosure. A control logic processor 20 obtains image data,either from a memory or from some other image source, such as viawireless transmission (e.g. Bluetooth), and provides the necessarytiming and control signals for forming the image in each eye of theviewer. Control logic processor 20 is in signal communication with alight module 30 and modulates the light from module 30 in order toprovide color image content. Frequency, duration, intensity and colormodulation is provided. According to an embodiment, light module 30provides modulated light from red, green, and blue laser diodes 32 r, 32g, and 32 b, respectively, coupled along an optical path and through anoptional objective lens L10 to a light guide, such as an optical fiber40. The modulated beam is characterized by pulses of laser light ofvariable color, duration and intensity. This light must beraster-scanned in order to form a recognizable image. Optical fiber 40directs the source light to a MEMS scanner apparatus 50, such as throughan optional collimator lens L12. The optional collimator lens L12 canalter focus in addition to beam size. Optional beam expanders canalternately be used. When energized, the MEMS scanner apparatus 50 scansby reflecting the light from optical fiber 40 through input lens 240,described in more detail subsequently, in a raster scanning pattern.Power is provided by a power source 22, such as a battery.

In embodiments that provide stereoscopic imaging, an optical fiber 40and scanner apparatus 50 can be provided for each eye E. (Only thesystem for a single eye E is shown in FIG. 1E for clarity.) The samelight module 30 can be used to generate images for both eyes, such assynchronously generating left- and right-eye modulated light;alternately, each eye E can have a separate light module 30, withappropriate image processing logic, provided by control logic processor20 and appropriate light handling components for the optical path thatforms each left-eye and right-eye image.

Light module 30 can be a commercially available modular component forgenerating a modulated beam of light according to input image data, suchas a pico-projector device from Microvision, Inc., Redmond, Wash. forexample. By way of example only, this device forms an image using lightfrom three primary color laser diodes, at 638 nm (Red), 517 nm (Green),and 450 nm (Blue). Other wavelengths can be used for primary colors. Thelasers can be low-power Class 1 devices, whose light can be directedtoward the eye of a viewer without concern for energy levels that areconsidered to be harmful. Light from each of the primary color laserscan be provided separately, so that red, green, and blue beams areprovided in rapid sequence. Alternately beams of the different primarywavelengths are combined for forming the color image. Techniques forbeam combination include the use of dichroic combiners, for example.Spot sizes for the light beams can be varied from each other, such asfor improved efficiency. The light beams can be collimated to providethe smallest optimal size or enlarged to overfill a small or large MEMSscanning mirror, as described in more detail subsequently. Beams can beconverted from a generally Gaussian profile to a flat-top profile forimproved beam homogeneity.

An exemplary optical fiber 40 can be a single-mode optical fiber. Thistype of light guide can be easily fitted into the band that is used forfitting the scanner apparatus 50 against the viewer's face, as describedsubsequently. The optical fiber can have an angled or otherwise shapedtermination, such as to help prevent back reflection. A single fiber canbe used for guiding light from all of the laser diodes 32 r, 32 g, 32 b.Alternately, three fibers can be used, spliced together to form a singlefiber at the light output at scanner apparatus 50.

The optical components of scanner apparatus 50 used in a particularwearable imaging apparatus can vary and may include, in addition to aMEMS scanner device, alternate types of reflective and refractive relayoptics, folding optics that may or may not provide optical power, andother components that are used to scan image content into eye E.Alternate components that may be part of scanner apparatus 50 aredescribed with reference to subsequent embodiments of the presentdisclosure.

The schematic diagram of FIG. 1F shows an exploded view of aconventional “pancake” optical system 90 of an eyepiece intended forforming an image for a viewer. The optical system uses polarization forfolding the light path of the modulated beam back upon itself andemploys reflective focusing optics with a curved mirror M1. Curvedmirror M1 defines an optical axis OA. The conventional image source 60is a cathode-ray tube or other emissive surface that provides atwo-dimensional (2-D) image field. Image source 60 is positioned at thefront focal surface of a curved mirror M1. A collimated beam is providedto the eye E from every field point. For the conventional pancake opticsdesign, magnification is very large and can be considered to beeffectively infinity.

The pancake system 90 works as follows: unpolarized light of a modulatedbeam from the CRT or other image source 60 is linearly polarized bypolarizer POL1 and converted to a left-hand circularly polarized lightby quarter wave plate QWP1. The light goes through semi-transparentcurved mirror M1; half of the light is reflected and lost. Mirror M1 isconsidered to be “partially transmissive” or “semi-transmissive” or“semi-transparent”, so that it transmits at least about 35% of theincident light from QWP1, preferably transmitting 50% of the incidentlight and reflecting 50% for peak efficiency. A partially transmissiveor semi-transparent curved mirror does not transmit more than 65% of theincident light.

The transmitted circularly polarized light goes through another QWP2 tobecome vertically linearly polarized light and is directed to areflective polarizer, polarization beam splitter PBS1, which reflectsmost of the light back towards the curved mirror M1. Reflected lightfrom PBS1 transits QWP2 again to become right-hand circularly polarized.The curved mirror M1 again reflects about half of the light and losesthe other half from transmission. The reflected polarized light frommirror M1 is now left-hand circularly polarized and is converted byquarter wave plate QWP2 into horizontally polarized light, passingthrough the reflective polarizer or polarization beam splitter PBS1 andthrough an optional cleaning polarizer POL3 into the eye E of theviewer. Each transit of the light through a quarter wave plate (QWP)retards the phase by a 45 degree shift, changing polarization state.

In spite of seemingly complex polarization and light-directingmechanisms, pancake optics function well, but with the penalty ofconsiderable loss of more than 75% of the light originally generatedfrom the light source 60. This inefficiency and substantial loss oflight makes the pancake optical configuration unusable for manyapplications with conventional sources of modulated light. TheApplicants, however, have recognized that this optical configuration canbe useful given the high levels of light attenuation using lasers withMEMs modulation, in which it is desirable to limit the light energyprovided to the viewer eye box.

Advantageously, this configuration uses the mirror on axis, without theneed to provide other means for separating the input beams into themirror from the output beams and without the requirement for folding oneor another portion of the optical path for image-forming. Conventionaltechniques employ a beam splitter for light path redirection between theeye and the mirror as is done, for example, in the Google-Glass™ systemby Google, Inc. or by tilting the curved mirror, thereby introducinglarge off axis aberrations.

Thus, the pancake design has the advantage of higher resolution over alarger field of view (FOV) as compared to a tilted mirror system. Thepancake optical design is smaller, with better eye relief as compared tosingle mirror system using a splitter.

Embodiment #1

The perspective view of FIG. 2A and side view of FIG. 2B show componentsof an imaging apparatus 200 for near-eye viewing using a 1:1 pupil relayapparatus 250 arrangement according to an embodiment of the presentdisclosure. This embodiment employs an optical “pancake” configurationas an optical relay system, using reflective components for beam shapingand focus that defines an optical axis and relays the input pupil to theoutput pupil. With the arrangement shown in FIGS. 2A and 2B, imagingapparatus 200 relays an input pupil P1 at image generator 212 to anoutput pupil P2 at the eye E of the viewer. Alternately stated, imagingapparatus 200 conveys a curved image at a focal surface 214 (wherein thegenerated image at focal surface 214 occupies the “object” positionrelative to the optics) to an image field at retina R. That is, inaddition to its role as pupil relay optics, apparatus 200 also images,to retina R, a curved aerial “object”, the real image formed at focalsurface 214, that is generated by the focused, scanned modulated beamfrom image generator 212.

An image generator 212 is provided by a scan mirror at an entrance pupilP1 that directs a focused modulated beam of light to form curved aerialimage at focal surface 214 as the “object” for subsequent imaging byimaging apparatus 200. The modulated light at the aerial image islinearly polarized and is directed to a polarizer 210 that transmitslight of a first polarization and reflects light of a secondpolarization that is orthogonal to the first polarization. Thetransmitted modulated light is directed through a quarter wave plate 216which provides the corresponding phase retardance and to a curved mirror220 that is partially reflective (nominally 50% reflective), partiallytransmissive (nominally 50% transmissive) and that serves as a type ofbeam splitter, focusing the modulated beam of light. Reflection of aportion of the light from mirror 220 reverses the circular polarizationof the light, which transmits through the quarter wave plate 216 whentraveling in the opposite direction. Light transmitted through mirror220 polarizes, absorbed by circular polarizer 230. Light reflected frommirror 220 has changed circular polarization and is reflected frompolarizer 210 and back through quarter wave plate 216. A portion of thislight travels through curved mirror 220 and transmits through forcleaning by optional circular polarizer 230. This cleaning helps toremove any leaked light having the orthogonal polarization that couldcause image ghosting. The collimated light from imaging apparatus 200 isdirected through the eye E of the viewer and to an output pupil P2 and,ultimately, to the retina R of the viewer, forming an image as shown.

The pancake optical system of FIG. 2B is a pupil relay apparatus 250having elements 210, 216, 220, and 230 similar to the FIG. 2Aarrangement. In this first embodiment there is air space between thecomponents, thus the term “air pancake” can be applied to this opticalarrangement.

Polarizer 210, disposed in the path of light from the scan mirror isformed to transmit incident light of a first polarization, incident at afirst angle that is divergent with respect to optical axis OA, towardthe curved mirror 220 surface. Polarizer 210 then reflects incidentlight from mirror 220 of a second polarization that is orthogonal to thefirst polarization of the transmitted incident light and at a secondangle with respect to a normal to the polarizer surface. The polarizer210 and curved mirror 220 are disposed along the optical path tocooperate, directing the modulated beam to polarizer 210 twice.Polarizer 210 is thus in the path of light to and from the curved mirror220 and folds the optical path back toward curved mirror 220. The lightthat exits the polarizer the second time is collimated and directedtoward pupil P2 and convergent with respect to an optical axis OA.

Unlike conventional arrangements wherein the pancake configuration formsan eyepiece to collimate the source, embodiments of the presentdisclosure use the pancake optics to relay the scanning mirror 212 inFIG. 2B to the iris 232 of the observer. This forms a pupil relay wherethe entrance pupil P1 on FIG. 2A is at the scanning mirror and P2 is theexit pupil at the eye. The pancake pupil magnification here is finite,preferably about −1 (minus one), for example.

The curved image at focal surface 214 and mirror 220 are substantiallyconcentric with respect to pupil P1, defined by curved mirror 220, withimage at focal surface 214 and mirror 220 sharing a center or axis ofcurvature at image generator 212. The axis of rotation of the scanmirror of the image generator 212 and the center of curvature of thecurved mirror 220 lie along the same line.

In the context of the present disclosure, two features are considered“substantially concentric” with respect to a pupil P1 or P2 when theyshare the same common axis of, and center of curvature to within 20% ofthe larger radial distance of the two curved features, so that anyslight difference in distance between their respective centers ofcurvature is less than 20% of the larger radial distance from that axisor center.

Polarizers 210 and 230 can be, for example, wire grid polarizers, suchas devices from Moxtek Inc., Orem, Utah.

The design of the optical path that is defined by the pupil relay opticsof the embodiments of the present disclosure is essentiallyaberration-free. The off-axis beams encounter exactly the same optics asthe on-axis beam and thus there are no off axis aberrations such ascoma, astigmatism, and distortion which commonly limit the performanceof optical systems. Thus, this display system is capable of providinglarge FOV. According to an embodiment, the system shown in FIGS. 2A and2B has a FOV of 43 degrees horizontally by 28 degrees vertically.

Note that in both FIGS. 2A and 2B, the retina R is represented ideallyas a flat surface, since the eye lens in this model is represented as anideal paraxial lens. When the eye is represented using a more realisticeye model, the retina is represented as a curved retina.

The embodiment shown in FIGS. 2A and 2B can also be used with the one toone pupil relay with the curvature of mirror 220 reversed along theoptical axis OA as shown in FIG. 2C. In pupil relay apparatus 260, theaerial image formed at focal surface 214 is of circularly polarizedlight. Nominally half of the light is rejected by the semi-transparentcurved mirror 220 and half is transmitted. The transmitted portionpasses through QWP 216 to become linearly polarized and is thusreflected from reflective polarizer 210 back to the curved mirror 220.This light is collimated and directed back to pupil P2 through polarizer210, in the orthogonal polarization which transmits through thepolarizer 210 towards iris 232. An optional cleaning polarizer 236 canbe used to eliminate light of the wrong polarization that may haveleaked through the reflective polarizer. Curved mirror 220 has itsradius of curvature centered at or centric with pupil P2. As with theFIG. 2A embodiment, the light first incident on polarizer 210 isdivergent with respect to optical axis OA. The light incident onpolarizer 210 the second time is collimated and direct along opticalaxis OA.

According to alternate embodiments using the FIGS. 2A-2C arrangement,curved mirror 220 is not a 50-50 semi-transparent mirror, but acts as acurved reflective polarizer, transmitting light of a first polarizationand reflecting light of the orthogonal polarization state. Flatreflective polarizer 210 is replaced with a semitransparent mirror. Oneskilled in the imaging arts can appreciate that additional variationsare possible using the curved mirror 220 as reflective polarizer andusing a flat, semi-transparent mirror.

Input Optics

The side schematic view of FIG. 3A and unfolded view of FIG. 3B showinput optics 240 that pre-focus the light that is directed throughpolarizer 210 and other components of the pupil relay in variousembodiments of the present disclosure. An objective lens 244 ispositioned in the path of the generated modulated light beam that isdirected to scan mirror 242. Lens 244 conditions the modulated light byexpanding the input beam and focusing it to a position between the scanmirror 242 and the pupil relay, defining and forming focal surface 214(FIGS. 2A, 2B). Objective lens 244 can consist of two elements, in theform of a cemented doublet or spaced apart, as shown subsequently. Anoff-the-shelf doublet can be used to correct for the axial color of therelay, assuming that three laser beams or more at different wavelengthsare used. Since the rest of the system is symmetrical and reflective,and with the axial color corrected by the input optics, there are noaxial or lateral color aberrations in this system. With respect to theembodiments shown in FIGS. 2A, 2B, 2C and following, input optics 240focus the light to form the curved aerial image at focal surface 214. Ascanning mirror 242 can be used to fold the optical path and to form a2-D image from the directed light beam.

By way of example only, FIG. 3C lists surface and lens characteristicsfor input optics 240 according to an embodiment of the presentdisclosure.

The light source can be a scanned laser or other solid state lightsource.

Embodiment #2

FIGS. 4A through 4I show different views of an all-glass pancakeconfiguration for a pupil relay apparatus 450 in an imaging apparatus400 for near-eye viewing according to an embodiment of the presentdisclosure. As with the previous embodiment of FIGS. 2A and 2B,apparatus 450 is a finite conjugate pupil relay working at amagnification of about −1. Focal surface 414 and curved input surface 92of lens L1 are substantially concentric with respect to pupil P1. Theoutput surface 420 of lens L1 and output surface 94 of lens L3 aresubstantially concentric with respect to pupil P2. In the optical pathdefined by pupil relay apparatus 450, polarizer 430 receives light of afirst polarization that is at a divergent angle with respect to opticalaxis OA and reflects this light back toward partially reflective curvedsurface 420 formed on lens L2, which focuses the light. Two transitsthrough QWP 424 change the polarization of the light beam to a secondpolarization state, orthogonal to the first polarization state atpolarizer 430. Polarizer 430 transmits the returned light, nowcollimated and directed toward pupil P2.

Some or all portions of pupil relay apparatus 450 can be positionedwithin the object focal length of the eye, 16.7 mm. This capabilityapplies for other pupil relay apparatus embodiments describedsubsequently.

FIG. 4B lists exemplary lens and polarizer surfaces for imagingapparatus 400 according to an embodiment of the present disclosure.

FIG. 4C is a perspective view showing imaging apparatus 400 with inputoptics 240 disposed at one side of scanning mirror 242.

Lenses L1, L2, and L3 may not be spherical in an embodiment of thepresent disclosure. FIG. 4D shows a vertical view of imaging apparatus400. Scanning is in the direction orthogonal to the plane of the page.

FIG. 4E shows a horizontal view of imaging apparatus 400. Scanning is inthe horizontal direction, in the plane parallel to the page.

As shown in FIG. 4F, the optical path can be folded in order to reducethe overall length and device footprint. Folding mirrors 454, 456 areshown by way of example.

FIG. 4G shows an exploded view of the pancake arrangement of pupil relayapparatus 450 of FIG. 4A, showing polarization states along the opticalpath that is defined by this optical system. Scanning mirror 412 atentrance pupil P1 directs light to form the curved aerial object atfocal surface 414. The light is circularly polarized, either beingcircularly polarized at the input beam or entering as linearly polarizedlight and rendered to circular polarization by an optional quarter waveplate (QWP) after the scanner mirror 412 (not shown). This light isrefracted through first lens L1 and through a partially reflectivesurface 420 to a second lens L2. The light then goes through quarterwaveplate QWP 424 and becomes linearly polarized (shown as verticallypolarized in FIG. 4G). This light encounters reflective polarizer 430and reflects back towards surface 420 passing again through QWP 424.About half of the light is then reflected by the semi-transparentsurface 420. The reflection off the curved 420 surface of lens L2collimates the beam which originated from its focused location as theaerial object at focal surface 414. The collimated light then goesthrough QWP 424 the third time, and becomes linearly polarized (shown ashorizontally polarized light in FIG. 4G.) This light passes throughpolarizer 430 and a third lens L3. This output light is directed fromsurface 420 to an iris 440 at exit pupil P2. Optionally a cleaninglinear absorptive polarizer (not shown) can be placed between lens L3and the iris at pupil P2. Focal surface 414 and input surface 96 of lensL1 are substantially concentric with input pupil P1. Output surfaces 98and 100 and mirror surface 420 are substantially concentric with pupilP2. Iris 440 is at pupil P2. Focal surface 414 is at the front focalsurface of mirror 420, reflected through polarizer 430.

FIGS. 4H and 4I show perspective views of pupil relay apparatus 450.

FIGS. 5A and 5B show side and front views, respectively, of imagingapparatus 400 on the face of a viewer. A conventional mount, such as aneyeglass frame, band, or other structure (not shown) can be provided forpositioning imaging apparatus 400 near to the viewer's eye, such aswithin the focal length of the eye lens.

Monocentric Embodiment

FIGS. 6A and 6B show side schematic views of an imaging apparatus 600 intwo configurations. In FIG. 6A, light from image generator 212, thescanning mirror at input pupil P1, is directed by input optics 240 to adiagonal polarizing beam splitter 610 that directs light through aquarter wave plate 616 and to a spherical curved mirror 620 that isconcentric with respect to pupil P2. Having transited the QWP 616 twice,light now has polarization orthogonal to that of the input beam. Lighttransmitted through the PBS 610 is directed to pupil P2, positioned ateye E. As with the FIG. 2A embodiment, the modulated light beam that isinitially incident on the polarizer, here polarizing beam splitter 610,is divergent and at a first polarization. Light returning to thepolarizing beam splitter 610 is collimated and at a second polarizationthat is orthogonal to the first polarization.

FIG. 6B is similar to FIG. 6A except that the light from pupil P1 isfirst transmitted, then reflected from PBS 610.

FIG. 6C shows a perspective view of imaging apparatus 600.

FIG. 6D shows a side view of imaging apparatus 600.

Polarizer 610 can be, for example, a wire grid polarizer, such as adevice from Moxtek Inc., Orem, Utah.

The FIG. 6A-6D embodiment is optically monocentric, with both inputpupil P1 (image generator 212) and output pupil P2 optically centricwith respect to the center of curvature of curved mirror 620. As can beseen from FIGS. 6A and 6B, pupils P1 and P2 are at the same opticalposition with respect to mirror 620.

FIGS. 7A-7D show different views of imaging apparatus 600 relative tothe viewer's eye.

Symmetrical Embodiment

The schematic side view of FIG. 8A and perspective view of FIG. 8B showa symmetrical arrangement modification of the imaging system of 4A, witha beam splitter 110. Beam splitter 110, which can be a polarization beamsplitter, helps to correct keystone distortion. When the input beamapproaches the scan mirror 242 as in FIG. 4C, at an angle, keystonedistortion can be induced, as shown for an outline of the image field inFIG. 8C. FIG. 8C shows uncorrected keystone distortion with a 43 by 25degree field of view when the incidence angle is 25 degrees from theaxis. The dashed line indicates a distortion free field. This distortioncan be corrected by electronically modifying the image data sent to theimaging system or by adding a slight aspheric distortion correctingelement (not shown) between scan mirror 242 and relay 450 optics. Beamsplitter 110 defines a light path with zero angle incidence intoscanning mirror 242 and the distortion shown on FIG. 8C is then reducedand made more symmetrical, as shown on FIG. 8D. Objective lens 244 hastwo lens elements, spaced apart by an air gap. An optional quarter waveplate 246 helps to reduce losses from beam splitter 110 when provided asa polarization beam splitter PBS. A second quarter wave plate 248changes the light from beam splitter 110 back to circularly polarizedlight. Mirror 220 can be a semi-transmissive mirror, as mirror surface420 on FIG. 4A, followed by another quarter wave plate 252. Reflectedon-axis light from mirror 220 is reflected from beamsplitter 110 anddiscarded. Elements L1, mirror 220, quarter wave plate 252, andpolarizer 230 may be a single cemented unit. There may be an air gapbetween the cemented unit and lens L2.

According to an embodiment shown in FIGS. 8A and 8B, the incomingmodulated beam from the light module 30 is S-polarized. In the opticalpath defined by pupil relay apparatus 450, this light is reflected frompolarization beam splitter 110 and directed to scan mirror 242 throughquarter wave plate (QWP) 246, becoming circularly polarized. The scanmirror 242 reflects the modulated beam back through QWP 246, changingthe polarization of the modulated beam to the P-polarization state.P-polarized light is then transmitted through beam splitter 110 andthrough QWP 248, which changes the polarization state to circularlypolarized. This light is conveyed through lens L1. A portion of thelight is reflected back along the optical axis OA from semi-transmissivemirror 220. This reflected light again transits QWP 248 and becomesS-polarized, so that it is reflected from beam splitter 110 anddiscarded. The portion of the modulated beam that transmits throughsemi-transmissive mirror 220, meanwhile, goes through another QWP 252,which changes its polarization to S-polarization state. This divergentlight is reflected by polarizer 230 and is then reflected from mirror220, now collimated and directed toward pupil P2. The collimated,modulated light, upon transiting QWP 252 a second time, is changed toP-polarization and transmits through polarizer 230 and to output lensL2.

The apparatus of the present disclosure provides an optical apparatusthat is suited for virtual reality (VR) or augmented reality (AR)viewing, as well as for mixed reality and smart glass viewing. Theimaging arrangement is essentially aberration free due to its opticalsymmetry. The apparatus is distinct from AR or VR optical configurationsbased on the use of an eyepiece, such as using catoptric optics, as wellas from refractive optics systems that collimate and magnify an imagesource such as an LCOS (Liquid crystal on silicon) display or a devicethat forms an image using an array of micromirror devices.

An embodiment of the present disclosure provides an FOV of at leastabout 40 degrees along the horizontal axis. Because it provides arelatively narrow beam of light, the imaging apparatus of the presentdisclosure can require eye tracking hardware to detect viewer eyemovement. Corresponding correction can be provided to compensate for eyemovement.

According to an embodiment of the present disclosure, there is providedan optical apparatus for near-eye viewing comprising: a laser lightsource energizable to direct a beam to a scan mirror; a curved mirrorsurface optically concentric with the scan mirror and partiallytransmissive; a first polarizer disposed between the scan mirror and thecurved mirror surface, the first polarizer having a first polarizationaxis; a quarter wave plate disposed between the polarizer and the curvedmirror surface; and a second polarizer disposed downstream from thecurved mirror and having a second polarization axis that is orthogonalto the first polarization axis.

The term “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any aspect described herein as “exemplary”is not necessarily to be construed as preferred or advantageous overother aspects.

The invention has been described in detail with particular reference toa presently preferred embodiment, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention. For example, although the above descriptionconcentrates on forming an image for one eye, it can be readilyunderstood that corresponding elements and logic are used for formingthe stereoscopic images needed to form and coordinate image content forboth right- and left-eye images, using methods familiar to those skilledin the stereoscopic imaging arts. The images that are formed can bestereoscopic or biocular, that is, with the same image content providedto both eyes for monoscopic display.

The presently disclosed embodiments are therefore considered in allrespects to be illustrative and not restrictive. The scope of theinvention is indicated by the appended claims, and all changes that comewithin the meaning and range of equivalents thereof are intended to beembraced therein.

What is claimed is:
 1. An optical apparatus worn by a viewer andcomprising: a laser light source energizable to direct a modulated beamtoward a scan mirror; an objective lens in the path of the modulatedbeam directed toward the scan mirror, wherein the objective lens and thescan mirror define a curved focal surface for the modulated beam; pupilrelay optics disposed to relay a first pupil at the scan mirror to asecond pupil at an eye lens of the viewer, the pupil relay opticsdefining an optical path between the first and second pupils, theoptical path comprising: (i) a curved mirror surface disposed totransmit substantially half of the light incident from the modulatedbeam and that has a first center of curvature at the first pupil; and(ii) a first polarizer disposed in the optical path to receive lightfrom the scan mirror and formed to reflect incident light of a firstpolarization toward the curved mirror surface and to transmit incidentlight of a second polarization, orthogonal to the first polarization,wherein the optical path defined by the pupil relay optics directs themodulated light beam twice to the first polarizer, and wherein themodulated light beam incident the second time on the first polarizer iscollimated and directed toward the second pupil.
 2. The opticalapparatus of claim 1 wherein the pupil relay optics further comprise asecond polarizer disposed in the path of the modulated light and formedto reflect incident light of the first polarization and transmitincident light of the second polarization.
 3. The optical apparatus ofclaim 1 wherein the pupil relay optics further comprise a secondpolarizer disposed in the path of the modulated light and formed toreflect incident light of the second polarization and transmit incidentlight of the first polarization.
 4. The optical apparatus of claim 1wherein the first polarizer is a polarization beam splitter.
 5. Theoptical apparatus of claim 1 wherein the first polarizer is a wire-gridpolarizer.
 6. The optical apparatus of claim 1 wherein the focal surfaceis concentric with the curved mirror surface.
 7. The optical apparatusof claim 1 wherein the curved mirror surface has a center of curvatureat the first pupil.
 8. The optical apparatus of claim 1 wherein thecurved mirror surface has a center of curvature at the second pupil. 9.The optical apparatus of claim 1 further comprising one or more quarterwave plates along the optical path.
 10. An optical apparatus worn by aviewer and comprising: a laser light source energizable to direct amodulated beam through an objective lens and toward a beam splitter,wherein the beam splitter directs a portion of the beam to a scanmirror, wherein the objective lens and the scan mirror define a curvedfocal surface for the modulated beam; pupil relay optics disposed torelay a first pupil at the scan mirror to a second pupil at an eye lensof the viewer, the pupil relay optics defining an optical path thatextends along an optical axis between the first and second pupils andcomprising: (i) a first lens in the path of light from the curved focalsurface; (ii) a curved mirror surface that transmits substantially halfof the light incident from the modulated beam and that has a firstcenter of curvature at the first pupil; and (iii) a first polarizerdisposed in the path of light from the scan mirror and formed to reflectincident light of a first polarization and at a convergent angle withrespect to the optical axis toward the curved mirror surface and totransmit incident light of a second polarization, wherein the secondpolarization is orthogonal to the first polarization, and wherein themodulated light beam incident the second time on the first polarizer iscollimated and directed toward the second pupil.
 11. The opticalapparatus of claim 10 wherein the beam splitter is a polarization beamsplitter.
 12. The optical apparatus of claim 11 further comprising afirst quarter wave plate disposed in the path of light between the beamsplitter and the scan mirror.
 13. The optical apparatus of claim 12further comprising a second quarter wave plate disposed along theoptical axis between the beam splitter and the first lens.
 14. Theoptical apparatus of claim 10 wherein the light from the laser lightsource is circularly polarized.
 15. An optical apparatus worn by aviewer and comprising: a laser light source energizable to direct amodulated beam through an objective lens and to a scan mirror to form acurved image; and pupil relay optics disposed to relay a first pupil atthe scan mirror to a second pupil at an eye lens of the viewer, thepupil relay optics comprising: (i) a first polarizer disposed in thepath of light from the scan mirror and formed to reflect incident lightof a first polarization and at a divergent angle and to transmitincident light of a second polarization, orthogonal to the firstpolarization, and collimated and directed toward the second pupil; (ii)a curved mirror surface that transmits substantially half of the lightincident from the first polarizer, wherein the curved mirror has acenter of curvature at both first and second pupils and wherein thecurved image is formed at a focal surface of the curved mirror; and(iii) a quarter wave plate in the path of light between the firstpolarizer and the curved mirror.
 16. The optical apparatus of claim 15further comprising a mount that disposes some portion or all of thepupil relay optics within the focal length of the viewer's eye lens.